One prior art method of centerless grinding cylindrical parts of rotation is to stack them and simultaneously grind a plurality of workpieces carried between the wheels of a centerless grinder. The workpieces are stacked end-to-end and "infeed", or plunge ground, by the grinding wheel. By progressive profiling of the regulating wheel, the cylindrical parts will have progressively stepped diameters, from a rough, stack-entering workpiece; to a smaller diameter, finished stack-exiting workpiece. After each grinding operation, the workpieces and regulating wheel are retracted from the grinding wheel and the workpiece stack is advanced to the next subsequent grinding station. However, one difficulty is inherent in this method of progressively producing the stacked workpieces, in that since the regulating wheel is linearly fed towards the grinding wheel, the same amount of grinding stock is removed from each workpiece in the same time interval.
When grinding, it is generally preferably to rough grind a relatively large amount of stock from a workpiece per unit time, shaping to a predetermined diameter, then later finish grinding the workpiece by removing a relatively small amount of stock per unit time from the predetermined intermediate diameter to the finished size, since wheel pressures and resulting deflections of the workpiece will be lessened during the finish grinding operation and the workpiece will tend to have a truer size and shape and better surface finish.
Applicant has obviated the difficulties inherent in the prior art design by employing a profiled regulating wheel which conforms generally to a stack of progressively reduced work sizes ranging from a largest size at an inlet end between the wheels to a smallest size at an outlet end between the wheels, wherein grinding feed is accomplished by pivoting the regulating wheelhead about a pivot point near the outlet end of the wheel. In this pivoting manner, the feed movement, or feed arc, is proportional to the distance from the pivot point to the successive pieces. Thus, a coarse-feed movement at the inlet end and fine-feed movement at the outlet end is achieved, with respective proportions therebetween along the wheel face. The pivot point, work support and regulating wheel are compensatingly movable in a linear direction towards the grinding wheel to adjust the work stack to the grinding wheel face after the grinding wheel has been conditioned by a suitable dressing means. The work engaging surfaces of the regulating and grinding wheels are angled to generate a conical workpiece at each station, so that all workpieces will remain coaxial and thereby be driven together with parallelism of the faces in contact maintained. "Over-square" parts (i.e. diameter-greater-than-length), would be likely candidates for this application because they are much narrower than the wheel--thus inefficient to grind one at a time, and large in diameter--meaning long infeed times that can better be broken up into progressive plunges. The finished included cone angle of a given work station is equivalent to the beginning cone angle of the next successive work station; that is, the beginning cone angle is the included angle formed by the grinding wheel face and the retracted regulating wheel face. By this method of progressive angle development of the successive workpiece stations, it is insured that as the regulating wheel is pivoted relative to the grinding wheel, the grind will start along the entire length of the workpiece, tending to cause a more efficient grind operation and a lessening of wheel wear.
If the wheel surfaces are parallel to the part axis (no progressive angle development) the parts will start grinding at one extreme end (toward the pivot) in a most unstable condition. Any roundness error introduced in this portion of the cycle must be generated out only after the stable support stage is reached.
It is therefore an object of the present invention to provide a relatively simple feed mechanism for a stack of workpieces, which accomplishes varying feed and rate increments at the respective workpieces from an inlet end to an outlet end between the wheels.
Another object of the present invention is to provide progressive angle development for a stack of workpieces to be infeed ground on a centerless grinding machine.
Still another object of the invention is to insure that, from the first contact of the wheel with the part until the end of the grind cycle, the port is completely supported along its entire length in the Vee formed by the work support blade and the regulating wheel.
A further object of the invention is to provide an efficient grind operation and a lessening of wheel wear when "station grinding" parts on a centerless grinder.